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World powers weighed tough options to end brutality in Syria on Tuesday amid the aftermath of the now-infamous massacre in Houla.

Politicians and opposition forces have been going back and forth over the future of the Kofi Annan peace initiative, the need for more diplomatic arm-twisting and even the prospect of military intervention as the world community cries for an end to the Syrian conflict.

The incident occurred on Friday in the Homs province town of Houla, where more than 100 people died. The United Nations says government forces went house to house and slaughtered men, women, and children. The Syrian government is blaming the violence on "terrorists."

The violence has left more than 12,000 slain since March 2011, according to one count, and tens of thousands of people have been displaced.

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What can the world do? Here are choices experts say the international community has:

Continue the U.N.-backed Kofi Annan plan:

U.N. and Arab League envoy Kofi Annan has proposed a six-point peace plan, ostensiblyaccepted by the Syrian government and opposition forces. It includes a cease-fire by all combatants, a call to pull back troops from major cities, and access for humanitarian groups. It also calls for a Syrian-led political process to resolve differences.

The cease-fire was forged April 12. A U.N. observation team is making sure the government is adhering to the plan and both sides are continuing the halt in violence.

But the future of this U.N. effort is in question because violence has continued despite the U.N. initiative. The Local Coordination Committees of Syria said on Saturday that more than 1,600 have been killed since Annan's initiative began.

Annan continued his diplomacy on Tuesday in a meeting with President Bashar al-Assad, urging adherence to the plan.

"We are at a tipping point," Annan said. "The Syrian people do not want the future to be one of bloodshed and division. Yet the killings continue and the abuses are still with us today. As I reminded the president, the international community will soon be reviewing the situation."

Andrew Tabler, Syria expert at the Washington Institute for Near East Policy said he thinks the denunciations over the massacre could prompt the regime to adhere to Annan's plan.

Elliott Abrams, senior fellow for Middle Eastern Studies at the Council on Foreign Relations, wrote on Tuesday the Annan plan "is in ruins."

"We will know in a few days whether Annan goes doggedly, indeed blindly, forward or salvages his own reputation by declaring his efforts at an end and demanding international action against Assad. Were he to do so, action might actually follow; it would be difficult for governments to turn away and dismiss his conclusions.

"So this week is a test for the former secretary-general. He may be remembered for this sorry turn in Syria -- or for demanding that governments face the truth and help the people of Syria put an end to the murderous Assad regime," Abrams said.

Jon Alterman, director of the Middle East Program at the Center for Strategic and International Studies, said "the utility" of the Annan plan is that it helped the world move forward on the issue. It won't necessarily change al-Assad's maneuverings, though.

"I think it's viable in determining greater international unity," Alterman said. "It may play a role in creating more international solidarity and a greater international determination to find some way out."

Provide military help:

While talk of military intervention is growing, a full-blown military operation like the one is Libya has not yet emerged.

Saudi Arabia, Qatar, and the Syrian Muslim Brotherhood have supplied rebels with "significant quantities of weapons" and Turkey has provided training and equipment, wrote James Traub, a fellow of the Center on International Cooperation and a columnist for Foreign Policy.com.

"Turkey will provide its territory for the training and organization of the Free Syrian Army, the United States will provide logistical and command-and-control assistance, and Gulf states will supply the hardware."

Traub wrote that the Obama administration "is said to be clandestinely helping direct arms to rebel forces" but "has admitted only to supplying communications equipment and other nonlethal assistance."

White House spokesman Jay Carney, said, "we do not believe that further militarization of the situation in Syria at this time is the right action."

The opposition has been fractious and decentralized, according to a number of experts.Traub said Annan, the United Nations, and others will help the opposition organize and grow, keeping the Syrian National Council "from collapsing into utter chaos, as it now threatens to do" and persuading the council, rebels, and the LCC "to work together."

Conservatives in the U.S. Congress and some voices in the Arab world have called for arming the opposition and criticized the Obama administration's stance as less than robust.

In March, Sens. John McCain, Joe Lieberman and Lindsey Graham not only called for military aid to the Free Syrian Army, but urged, if requested by the opposition, a U.S.-led effort to protect civilian population centers with airstrikes.

Tabler from the Washington Institute for Near East Policy said the Houla massacre and constant regime violence could bring tougher action and some sort of intervention plan.

There's a general understanding emerging that al-Assad is not going to go without some sort of more direct action, Tabler said.

"The Iranians and the Russians have been arming the Syrian regimes to the teeth while they mow down the Syrian people. It's very hard to stand by and do nothing."

"I think it involves backing the opposition, after that, it is the creation of safe zones, then there could be airstrikes," Tabler said.

Aram Nerguizian, visiting fellow, Burke Chair in Strategy, at the Center for Strategic and International Studies, raised questions about military intervention, saying the logistical and military challenges would be significant, and the resources required to produce a political outcome that is anything but certain in Syria would be massive.

The regime continues to maintain strong military backing and support among several sectors of society, such as the Alawites that predominate in the army, other minorities, and business people.

A key challenge at present is that the opposition remains "all but leaderless" and there is no counterpart to al-Assad. And, he said, the international community remains divided.

As a result, there has been low-intensity pressure and pragmatism with sanctions and logistic support to a fledgling opposition. But world powers have been and are stopping short of much deeper escalation.

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"There's an attempt to stick to a formula," Nerguizian said. He said he thinks diplomacy will "muddle along" and that the conflict will continue "to draw out over time."

Alterman, from CSIS, warned against impatience and calls for instant change. Citing U.S. support for other long wars against regimes, he said planners need to think about longer time-frames.

"In many ways we've been driven by daily developments, and the problem with that is a lot of options take years to have an effect," he said.

"People want to know what can you do this week that can make him go next week."

He said it's important to gauge long-term effects, impacts of neighbors, and amassed support and realize that changing the status quo could be disastrous, like the sectarian violence during the last decade in Iraq.

"You have to have your eyes wide open," he said.

"Relying on weapons to dislodge this government is a dangerous excercise because it continues to move the conflict into a sphere where the Assad government will have an advantage," he said. "The more this is an armed battle, the more it moves in the direction of the Assad government."

Rafif Jouejati, spokeswoman for the Local Coordination Committees of Syria, a network of opposition members, said the international community should stop saying that military action is off the table.

"Such language only gives Assad the green light and renders condemnations useless. By sending Assad the message that military options are being considered, the international community can be far more effective in putting an end to this modern-day Holocaust," she said.

Ratchet up diplomatic pressure:

For months countries across the globe have been using diplomatic and economic pressure, such as sanctions to force the al-Assad regime to end its crackdown. On Tuesday, a number of countries announced they were expelling Syrian diplomats in a coordinated move, reflecting the international outrage toward a massacre in the town of Houla.

The Netherlands, the United States, Australia, Great Britain, France, Germany, Italy, Spain and Canada said they were expelling some Syrian diplomats. In some cases, it was just the ambassadors; in others, numerous diplomats were expelled.

"The expulsion of diplomats is very significant and represents concrete action to accompany the international community's strong words of condemnation. The expulsions also further destroy any remaining semblance of legitimacy the Assad regime may have thought it had," Jouejati said.

"Obviously no single action like that diplomatic action (expulsions) stops the regime from its brutal behavior, but it is a cumulative effort," Carney, the White House spokesman, said. "And it is important in that it demonstrates just how isolated the Assad regime has become, how far afield from the international community it has positioned itself in the brutal pursuit of its own continued existence at any cost."

Another international diplomatic presence is the Friends of Syria -- a group of countries, led by Western and Arab nations dealing with the crisis. The group formed after Russia and China blocked tough action against Syria in the U.N. Security Council.

The group met in Tunisia in February and Turkey in April and will hold another meeting this July in Paris.

Those powers are hoping that Russia, which has long backed Syria, will exert influence on al-Assad. Russia, the staunchest defender of the Syrian regime on the council, signed on to a statement that condemned the Syrian government for its "outrageous use of force against (the) civilian population."

"We hope the international community will take things a step further and exert pressure on Russia to stop delivering weapons to Assad. For example, the recent delivery of $100 million in Russian weapons -- which in turn will be used against civilians -- could have been stopped through targeted pressure and sanctions on Russia," Jouejati said.

Iran is a strong backer of the Syrian regime. Nerguizian said talks between world powers and Iran over Tehran's nuclear aspirations have an impact on Tehran, Damascus and the region.

The negotiators, who met in Baghdad last week, meet again next month in Moscow. Western powers have initiated tough sanctions against Iran, including its oil production, to stop it from developing nuclear weapons. Iran has denied it is pursuing nuclear weaponry program.

The nuclear talks matter, Nerguizian said, "because applying or relieving pressure on the Assad regime at the international level is one way to affect the leadership in Tehran. The negotiations also matter because they will impact the scale and shape of an increasingly deepening Sunni-Shiite regional struggle that pits the Gulf states led by Saudi Arabia against Iran and its allies, especially Syria and Hezbollah in Lebanon."

Forge a deal to force al-Assad's departure:

One proposal that has emerged is a so-called "Yemen model." This is in reference to the Gulf Arab plan that led to the departure of unpopular Yemeni President Ali Abdullah Saleh. The option was broached in a January Chatham House think-tank report and came up in a New York Times story on Sunday.

"The regime weakens to the point that it realizes it cannot continue to remain in power. This leads to a Yemen-style deal whereby the Assad family and their closest cronies leave the country in return for immunity," the Chatham House report said.

In this scenario, The New York Times says President Obama would push for a "negotiated political settlement that would satisfy Syrian opposition groups but that could leave remnants of Mr. Assad's government in place" based on the Syrian model.

"The success of the plan hinges on Russia, one of Mr. Assad's staunchest allies, which has strongly opposed his removal," the report said.

Nerguizian said such a move wouldn't change grass-roots sectarian differences in the religiously and ethnically diverse population.

Syria and Yemen are different, Nerguizian said. Yemen is largely tribal with a mix of Sunnis and Shiites. Saleh did a far better job of sharing power and patronage outside his immediate and nearer power circles than al-Assad did and does.

Also the Alawites -- which dominate in the Syrian ruling structure -- are a small minority, whereas Sunnis account for some 70% -- so nowhere near the kind of internal dynamics as Yemen, and on a different evolutionary trajectory, he said.

"A Yemen model wouldn't change much in Syria, where there would be sectarian differences and pressures (pressures which define the struggle for power, and which any deal would have to factor in) in the religiously and ethnically diverse population. "

In fact, Nerguizian said, "events have spiraled so far out of control in Syria that an "Algerian model or an Iraq model are "far more plausible."

He was referring to Algeria's civil war in the '90s that left more than 150,000 people dead when an "intransigent regime" battled against mainly Islamist opposition forces. "The conflict brutally metastasized Algerian politics and the country continues to battle with the legacy of the conflict."

He said an "Iraq model," where countries accept and even institutionalize their divisions is also possible.

"We saw this in Iraq, Lebanon and even in Bahrain where these cleavages affect many aspects of political life. This model would see the institutionalization of sectarian politics in a loose confederal system that seeks to protect the interests of competing minority groups. This model too is inherently unstable and tends to require strong internal and external support for a settlement over a long period of time."